Many of α,β-unsaturated carboxylic acids are industrially useful. For example, acrylic acid or methacrylic acid is being used in a considerable amount for the application such as a raw material of synthetic resins. Although examples include gas-phase oxidation and liquid-phase oxidation of isobutene and a method by way of acetone cyanohydrin as a method for producing methacrylic acid, there is not a specifically advantageous method and methacrylic acid has been industrially produced by these several methods.
There has been many researches on a catalyst and a method for producing an α,β-unsaturated carboxylic acid through liquid-phase oxidation of an olefin or an α,β-unsaturated aldehyde with molecular oxygen. Examples include a method in the presence of gold supported catalyst (Patent Document 1), a method using a palladium metal catalyst (Patent Documents 2 to 6) and a method using a molybdenum compound and a palladium catalyst (Patent Document 7).
The catalysts disclosed in Patent Documents 2 to 7 contain palladium as a component of a catalyst, however, there is no description concerning particle diameter of palladium. Further, some of the catalysts disclosed in Patent Documents 1 to 7 are supported on a carrier such as activated carbon, alumina or silica. However, as for physical properties of these carriers, there is merely one description in Patent Document 1 as “it is preferable to use a hydrophobic carrier or a conventional carrier subjected to hydrophobic treatment”, and there are no other descriptions, in those documents, referring to physical properties of these carriers.
Patent Document 1: Japanese Patent Application Laid-Open No. 2001-172,222.
Patent Document 2: Japanese Patent Application Laid-Open No. 60-155,148.
Patent Document 3: Japanese Patent Application Laid-Open No. 60-139,341.
Patent Document 4: Japanese Patent Application Laid-Open No. 60-139,643.
Patent Document 5: U.S. Pat. No. 4,435,598.
Patent Document 6: International Publication No. WO 02/083,299.
Patent Document 7: Japanese Patent Application Laid-Open No. 56-59,722.